Human growth data from Guatemala were analyzed to test the hypothesis that the degree of sexual size dimorphism (SSD) may be an indicator of environmental quality. The sample consists of Guatemalan school children (6 to 16.99 years of age) distributed into high, middle and low socioeconomic status (SES) groups. SSD was calculated as a ratio of male to female height, with higher values implying a greater degree of dimorphism; while SES was used as a proxy for environmental quality. Results suggest that between 6 and 11.99 years of age, SSD remains constant for all SES groups. Starting from 12 years of age, SSD increases for both high and middle SES groups. However, in children that belong to the low SES group, SSD stays low until 13 years of age, after which SSD shows lower increase than in higher SES groups. Analysis of growth data for females and males suggests that low levels of SSD in the low SES group after 12 years of age can be related to developmental delays and a slower rate of growth in the lower SES males. This adds support to the “fragile male” hypothesis, which posits greater male sensitivity to a suboptimal environment during growth and development.